The idea has spread to dozens of cities and neighborhoods around the country. Atlanta, Oakland, Calif., Phoenix, and Hyattsville, Md., all boast their own little galleries. The FLAGs, as they call themselves, are close cousins of the Little Free Library. Some have criticized little libraries as evidence of gentrification and say they are nothing more than stockpiles of bad, unwanted books. But the little art gallery, where anyone from neighborhood children to retired artists to working professionals can swap fun-sized art, is much more personal and, ideally, more intentional. Books come and go from little libraries with relative anonymity. Here, there is an exchange from one artist’s fingertips to another’s — literally.